The present disclosure generally relates to solid-state image sensor devices, and specifically to testing of pixels in such devices.
Solid-state image sensor devices, such as charge-coupled devices (CCD) or active pixel sensors (APS), are widely used to capture images. Wide use of these devices has led to a demand for faster and more reliable testing of pixel arrays on these devices.
The pixel arrays may be excited with a uniform or patterned illumination. The response is often measured or evaluated manually by visually inspecting a screen projected on a monitor. However, visual inspection may require a limited number of inspectors who are capable of making precise and consistent qualitative judgment. Furthermore, the inspection process may be time-consuming.
The present disclosure describes an image sensor testing system. The system includes a differencing element, first and second comparators, and a counter.
The differencing element is arranged to provide a difference value between a given pixel value and a pixel stream value. The first comparator operates to compare the difference value with at least one tolerance value. The counter is configured to increment a count when the difference value exceeds at least one tolerance value. The second comparator is configured to indicate a sensor as having failed if the count exceeds at least one threshold value.
The present disclosure also describes a method for testing an image sensor. The method includes computing a difference between a given pixel value and a pixel stream value, and comparing the difference with a specified tolerance value. A count is incremented when the difference exceeds the specified tolerance value. The image sensor is indicated as having failed the test if the count exceeds a specified threshold value.
The present disclosure further describes an image sensor, which includes a pixel array, a readout circuit, a controller, and a sensor testing system. The pixel array includes pixels arranged in an array. Each pixel is configured to sense light coming from a direction corresponding to a position of each pixel. The readout circuit operates to read out signals stored in the pixel array. The controller is configured to provide timing and control signals to enable the read out of the signals. The sensor testing system provides similar functions as the image sensor testing system described above.